1. Technical Field
The present invention relates to ink compositions and particularly relates to an ink composition useful in achieving a recorded image with good light fastness without impairing the hue of a colorant.
2. Related Art
In recent years, records have been obtained in such a manner that color images are formed by ink jet recording using a plurality of color ink compositions. In usual, the color images are formed using three ink compositions, that is, a yellow ink composition, a magenta ink composition, and a cyan ink composition or four ink compositions, that is, the three ink composition and a black ink composition. Alternatively, the color images are formed using six ink compositions, that is, the four ink compositions, a light cyan ink composition, and a light magenta ink composition or seven ink compositions, that is, the six ink compositions and a dark yellow ink composition in some cases.
The ink compositions used to form the color images individually need to have good color developability, combinations of some of the ink compositions need to exhibit good intermediate colors, and records obtained from the ink compositions need to not be discolored during storage.
Improvements have been continually made for heads, ink compositions, recording techniques, and media used to print “photographic quality” images with color ink jet printers; hence, recently obtained images are comparable in level to “silver-halide photographs” and have “photographic quality”. Furthermore, attempts have been made to improve the storage stability of obtained images as ink compositions and media are improved. In particular, the obtained images have improved light fastness satisfactory for practical use (see JP-A-2000-290559 and JP-A-2001-288392); however, the obtained images have not been comparable in light fastness to silver-halide photographs. Light fastness is usually evaluated on the basis of the fading rate of a yellow (Y) pattern, magenta (M) pattern, and cyan (C) pattern having an optical density of about 1.0. In the case of evaluating the light fastness of ink compositions loaded into currently commercially available printers by the above evaluation method, the light fastness of magenta ink compositions is lowest; hence, the magenta ink compositions often determine the lifetime of ink sets. Therefore, the improvement of the light fastness of the magenta ink compositions is effective in enhancing the light fastness of photographic images and the lifetime of ink sets.
Prints prepared using the ink compositions are placed not only indoors but also outdoors and therefore are exposed to not only indoor light but also sun light. Thus, there is a need to develop an ink composition having excellent light fastness.
Proposed examples of colorants having excellent light fastness include a compound (an azo dye) disclosed in JP-A-2002-371079 and a compound (an anthrapyridone dye) disclosed in JP-A-2002-332419. A magenta ink composition which contains a combination of two types of colorants and which has excellent light fastness has been proposed (see JP-A-2005-105136). Any ink composition useful in achieving a recorded image with good light fastness without impairing the hue of a colorant has not been known as far as the inventors know.